CR250R Compression

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riding around the other day after buying a used 97 Cr250R, rode it around for about 3 hours...noticed the bike had died. figured it was the gas that ran out...kicked it again rode it for about 15 feet down a trail and it was overheated spraying white smoke from the front of the bike...somewhat loss of compression now, checked the top end which is fine. checked the radiator and there was no water...buddy thinks the water jacket may be cracked any ideas? its not seized because the piston moves up and down just fine, there is spark. carb is working fine its spraying fuel. everything seems to be fine. i'm about to take apart the jug, and left/right crank cases to check for damage...

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right, exactly what i was thinking, if the head gasket is all crazy looking i'll just replace it...but i would like to figure out why it overheated to begin...i live in texas it was around 110 degree's i was an idiot and didn't check the coolant level before riding...maybe there was NO water in it to begin with...the water pump propeller seems to be turning just fine.

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Hey guys. I took apart the top end today. Found major scoring on the back of the piston and the inside back of the cylinder facing the air filter as if someone had been riding it with no air filter. ALSO found that since the overheat that the reed valves are completely melated and blocking air gas flow. Pretty sure with new seals rebore of cylinder new piston and new reed valves I should be good. I need to figure out why it overheated to begin with.